"Some orders we see are daisy chains, where we get a subpoena for information on one person and then they want all the information on the persons calling or called by them," Sussman said. "We don't think these orders should include the pizza guy."

Cell providers are happy to help police in emergencies, such as finding a teen driver who's driven into a deep ditch, said Sussmann during a panel discussion at the Computers, Freedom and Privacy conference.

Real-time tracking of cell phones is possible because mobile phones are constantly sending data to cell towers, which allows incoming calls to be routed correctly. The towers record the strength of the signal along with the side of the tower the signal is coming from. This allows the phone's position to be easily triangulated to within a few hundred yards.

But the legal grounds for obtaining a tracking order is murky -- not surprising since technology often outpaces legislation. The panel agreed that Congress should write rules governing what level of suspicion cops need to have before tracking people through their cell phones

The Justice Department has argued that a combination of wiretap laws governing stored communications like voicemail, plus a law that lets them learn the phone numbers people dial, allows them to track people without having probable cause.

Investigators commonly bundle a request to track cell phones with orders to capture the dialing information of incoming and outgoing calls from landline or cell phones. Those orders only require investigators to certify that the information is likely relevant to an ongoing investigation.

Since most of the orders are filed under seal to prevent targets from learning they will soon be tracked, little was known of the scope of, and legal justifications for, cell tracking orders.

Kevin Bankston, a lawyer with the Electronic Frontier Foundation, said during the panel discussion: "We've seen an avalanche of decisions rejecting the government's hybrid theory. For several years, the DOJ has been successfully pulling the wool over the eyes of magistrates."

Some of the legal uncertainty may be resolved soon as the Justice Department has filed an objection in at least one case, according to Bankston.

Not everyone on the panel thought cell tracking without probable cause was a bad thing.

"What's all the fuss?" said Catholic University of America law professor Clifford Fishman. "The government has legitimate reasons to follow people. This is the technology law enforcement needs to use to get probable cause to search you, arrest you and throw you in jail."

Fishman, a former prosecutor who spent eight years prosecuting drug crimes in New York state, said it was reasonable for police to track a suspect's girlfriend to see if she would lead to his hide-out.

As for concerns that cell phones could be used for widespread tracking since it requires almost no manpower, panelist and law blogger Orin Kerr said such fears will dissipate once people understand that calls don't get to their phones by magic.

"After you get comfortable with the technology, it just becomes more commonly understood that when I turn this thing on I'm creating data and I wouldn't be surprised if our view of what the privacy threshold should be will change over time," Kerr said.

Though the conference program promised that a DEA agent would be on the panel, the Justice Department nixed his participation at the last minute, even though he was only booked to talk about how cell tracking information was useful to prosecutions, according to Bankston.